This invention relates generally to vacuum chambers, such as dry etch plasma chambers used in semiconductor processing, and particularly to controlling the pressure of such chambers.
There are four basic operations in semiconductor processing, layering, patterning, doping, and heat treatments. Layering is the operation used to add thin layers to the surface of a semiconductor wafer. Patterning is the series of steps that results in the removal of selected portions of the layers added in layering. Doping is the process that puts specific amounts of dopants in the wafer surface through openings in the surface layers. Finally, heat treatments are the operations in which the wafer is heated and cooled to achieve specific results, where no additional material is added or removed from the wafer.
Of these four basic operations, patterning is typically the most critical. The patterning operation creates the surface parts of the devices that make up a circuit on the semiconductor wafer. The operation sets the critical dimensions of these devices. Errors during patterning can cause distorted or misplaced defects that result in changes in the electrical function of the device, as well as device defects.
The patterning process is also known by the terms photomasking, masking, photolithography, and microlithography. The process is a multi-step process similar to photography or stenciling. The required pattern is first formed in photomasks and transferred into the surface layers of the semiconductor wafer. This is shown by reference to FIGS. 1A and 1B. In FIG. 1A, the wafer 100 has an oxide layer 102 and a photoresist layer 104. A mask 106 is precisely aligned over the wafer 100, and the photoresist 104 is exposed, as indicated by the arrows 108. This causes the exposure of the photoresist layer 104, except for the part 110 that was masked by the part 112 of the mask 106. In FIG. 1B, the unexposed part 110 of the photoresist layer 104 is removed, creating a hole 114 in the photoresist layer 104.
Next, a second transfer takes place from the photoresist layer 104 into the oxide layer 102. This is shown in FIG. 1C, where the hole 114 extends through both the photoresist layer 104 and the oxide layer 102. The transfer occurs when etchants remove the portion of the wafer""s top layer that is not covered by photoresist. The chemistry of photoresists is such that they do not dissolve, or dissolve very slowly, in the chemical etching solutions. Finally, the photoresist layer 104 is removed, as shown in FIG. 1D, such that only the wafer 100 and the oxide layer 102 with the hole 114 remains.
The removal of the photoresist layer can be accomplished by either wet or dry etching. Wet etching refers to the use of wet chemical processing to remove the photoresist. The chemicals are placed on the surface of the wafer, or the wafer itself is submerged in the chemicals. Dry etching refers to the use of plasma stripping, using a gas such as oxygen (O2), C2F6 and O2, or another gas. Whereas wet etching is a low-temperature process, dry etching is typically a high-temperature process.
One type of dry etching process is shown in FIG. 2. Within the chamber 200, a semiconductor wafer 202 sits on a number of pins 208, 210, and 212, such that the wafer rests against a heater block 216. This position of the wafer 202 resting against the block 216 is referred to as the pin down position. Gas is introduced at insertion point 206, where the showerhead 204 sprays the gas onto the plasma 218, which is situated within the grounded grid 214. The plasma 218 energizes the gas to a high-energy state, which in turn oxidizes the resist components to gases that are removed from the chamber 200 by a vacuum pump (not shown in FIG. 2). Dry etching is advantageous to wet etching for resist stripping because it eliminates the use of wet hoods and the handling of chemicals.
For the dry etch process to work properly, the pressure within the chamber must be able to be controlled in a precise manner. However, existing pressure control mechanisms are less than desirable. They make it difficult to control chamber pressure in a linear manner. Furthermore, their machine parts are heavy, taking up great amounts of space, and move slowly, rendering pressure control a slow process, particularly to stabilize the pressure at a desired level.
FIG. 3 shows one type of existing plasma chamber pressure control mechanism 300, which utilizes a throttle valve design. The pressure chamber 304 opens to a cavity 302 through an opening 314, in which a tapered valve 306 is situated. The tapered valve 306 is connected to a rod 308. Vertical movement of the rod 308, as indicated by the arrow 310, is possible through a controller 312. Such vertical movement causes the valve 306 to expose more or less of the opening 314, allowing control of the pressure in the chamber 304.
For example, where the valve 306 is positioned higher within the chamber 304, more of the opening 314 is exposed, causing lower chamber pressure. This is shown in the vertical view of FIG. 4A, where the valve 306 occupies less of the opening 314, exposing a larger part of the opening 314, as indicated by the reference number 402. However, where the valve 306 is positioned lower within the chamber 304, less of the opening 314 is exposed, causing higher chamber pressure. This is shown in the vertical view of FIG. 4B, where the valve 306 occupies more of the opening 314, exposing a smaller part of the opening 314, as indicated by the reference number 404.
FIG. 5 shows another type of existing plasma chamber pressure control mechanism 500, which also utilizes a throttle valve design. The pressure chamber 504 opens to a cavity 502 through an opening defined between the spacers 508 and 510, in which a valve 506 is situated. Vertical movement of the valve 506 causes the valve 506 to expose more or less of the opening defined between the spacers 508 and 510, allowing control of the pressure in the chamber 504.
For example, where the valve 506 is positioned higher within the cavity 502, more of the opening is exposed, causing lower chamber pressure. This is shown in the vertical view of FIG. 6A, where a relatively large part of the opening, indicated by the reference numbers 602 and 604, is exposed. However, where the valve 506 is positioned lower within the cavity 502, less of the opening is exposed, causing higher chamber pressure. This is shown in the vertical view of FIG. 6B, where a relatively small part of the opening, indicated by the reference numbers 606 and 608, is exposed.
FIG. 7 shows an exploded view of a final type of existing plasma chamber pressure control mechanism 700, which utilizes a pendular valve design. The pressure chamber 712 has an opening 714, which is concentrically positioned along the vertical axis 702 over the opening 706 of the top flange 704. The pendular valve 708 has an opening 710 that allows access of the opening 714 of the chamber 712 to the opening 706 of the flange 704 when the opening 710 is concentrically aligned over the openings 714 and 706. However, the valve 708 is rotatable along the vertical axis 718, as indicated by the arrow 716, such that more or less of the opening 710 can be exposed, meaning that more or less of the opening 714 of the chamber 712 is allowed access to the opening 706 of the top flange 704.
For example, where the opening 710 of the valve 708 is positioned relatively more concentrically over the opening 714 of the chamber 712, more of the opening 706 of the flange 704 is exposed, causing lower chamber pressure. This is shown in the vertical view of FIG. 8A, where the opening 710 is relatively more concentrically positioned over the opening 714, causing a relatively large access area 802 to the opening 706 (not shown in FIG. 8A), for lower chamber pressure. The large access area 802 is the area of overlap, or intersection, between the openings 710 and 714.
However, where the opening 710 of the valve 708 is positioned relatively less concentrically over the opening 714 of the chamber 712, less of the opening 706 of the flange 704 is exposed, causing higher chamber pressure. This is shown in the vertical view of FIG. 8B, where the opening 710 is relatively less concentrically positioned over the opening 714, causing a relative small access area 804 to the opening 706 (not shown in FIG. 8A), for higher chamber pressure. The small access area 804 is the area of overlap, or intersection, between the openings 710 and 714.
The plasma chamber pressure control mechanisms of FIGS. 3, 5, and 7 that have been described exhibit the mentioned disadvantages of existing chamber pressure control mechanisms. Therefore, there is a need to control chamber pressure in a linear manner. There is also a need for a pressure control mechanism that does not require a heavy valve and associated machinery, such that the mechanism does not use a large amount of space. Finally, there is a need for a pressure control mechanism that moves relatively quickly, rendering pressure control a faster process, particularly to stabilize the pressure at a desired level. For these and other reasons, there is a need for the present invention.
Linearly controlling the pressure of a vacuum chamber, such as a plasma etch chamber used in semiconductor processing, is disclosed. A plasma etch chamber pressure control mechanism of the invention includes an aperture diaphragm and a number of aperture blades rotatably mounted on the aperture diaphragm. The diaphragm defines a contractible and expandable aperture for controlling the pressure of the chamber. Rotation of the aperture blades in a first direction, such as counter-clockwise, contracts the aperture, increasing the pressure of the chamber. Rotation of the aperture blades in a second direction opposite to the first direction, such as clockwise, expands the aperture, decreasing the pressure of the chamber.
The mechanism can also include two rotatable circular frames. The first frame is around the aperture diaphragm and has a number of inward facing gear teeth. Gear teeth of circular gears corresponding to the aperture blades, and rotatably mounting the blades to the diaphragm, interlock with the inward-facing gear teeth of the first frame. Rotation of the frame in the first direction causes the rotation of the blades in the first direction, and vice-versa. The first frame preferably insulates the aperture diaphragm and the aperture blades in an airtight manner.
The second frame is around the first frame, and interacts with the first frame to cause the rotation of the first frame indirectly in the direction that the second frame is directly rotated. Both frames may include magnets substantially equally spaced around them, where each magnet of the second frame has a polarity opposite to that of a corresponding magnet of the first frame. Directly rotating the second frame causes indirect rotation of the first frame through interaction among the magnets of the second frame with magnets of the first frame. A motor may be used to directly rotate the second frame.
The invention provides for advantages not found within the prior art. Plasma chamber pressure may be controlled linearly, because the aperture may be expanded and contracted linearly. In the embodiment where there are two frames, the outer frame is directly controlled with a motor, such that the motor and the frames do not require a large amount of space. The aperture may also be quickly contracted and expanded, stabilizing the chamber pressure at a desired level faster than in the prior art. Still other advantages, aspects, and embodiments of the invention will become apparent by reading the detailed description that follows, and by referencing the attached drawings.